Kreb's Cycle.

- discovered by Sir Hans Krebs (1900-81) in 1937

- takes place in the mitochrondial matrix
- part of cellular respiration

- is an eight-step process with each step catalyzed by a specific enzyme

- the original glucose molecule is entirely consumed at the end of the cycle

 Steps of the Kreb's Cycle:

1. acetyl group (2C) condenses with oxaloacetate (4C) and forms citrate (6C)
2. citrate (6C) is rearranged to isocitrate (6C)
3. carbon dioxide is lost, NAD+ is reduced to NADH, isocitrate becomes alpha-ketoglutarate (5C)
4. carbon dioxide is lost, coenzyme A is added, two hydrogen atoms reduce to NAD+ to NADH, and it becomes succinyl-CoA. (4C)
5. ATP is formed by substrate level phosphorylation, coenzyme A is released and succinate (4C) is formed.
6. two hydrogen atmos reduce from NAD to NADH2 and is converted into fumerate (4C)
7. fumerate to maltate (4C)
8. two hydrogen atoms reduce NAD+ to NADH, and is converted into oxaloacetate (4C)

- cyclic process because the oxaloacetate is a product and soon becomes a reactant

- energy is harvested in steps 3, 4, 5, 6, 8.

- NADH and FADH2 molecules will eventually be transferred to ATP to the last stage of cellular respiration

- all six carbon atoms of glucose have been oxidized and released as metabolic waste as carbon dioxide